DISTRIBUTION OF SUBSTANCE-P-CONTAINING AND CATECHOLAMINERGIC NERVE-FIBERS IN THE RABBIT CAROTID-BODY - AN IMMUNOHISTOCHEMICAL STUDY IN COMBINATION WITH CATECHOLAMINE FLUORESCENT HISTOCHEMISTRY

The distribution of substance P (SP)-immunoreactive nerve fibers in th e rabbit carotid body was studied in combination with catecholamine au tofluorescence images of sections where SP immunoreactivity was confir med. Immunoreactivity for SP was found in nerve fibers distributed in the parenchyma of the carotid body. No glomus cells with SP immunoreac tivity were observed in the carotid body. On comparing the distributio n of SP-immunoreactive fibers with the catecholamine autofluorescence image in a single section, most SP fibers appeared associated with the fluorescent glomus cells, and were located around clusters of them. T hese results support the suggestion that SP fibers in the cat and rat carotid bodies are involved in chemosensory mechanisms. Furthermore, a survey of the present results and previous ones reported by other wor kers indicates that SP may be an essential neuropeptide in chemorecept or organs in most vertebrates from amphibians on upwards evolutionally . In addition, the courses of some catecholaminergic fibers precisely agreed with those of some SP fibers. This suggests that certain sympat hetic nerve fibers also contain SP.